A likely explanation is that for small expected counts, the estimate of between study heterogeneity is very often 0 or close to 0, and this attenuates any differences between scenarios with smaller and larger simulated heterogeneity.

From: Results

Cover of Simulation-Based Comparison of Methods for Meta-Analysis of Proportions and Rates
Simulation-Based Comparison of Methods for Meta-Analysis of Proportions and Rates [Internet].
Trikalinos TA, Trow P, Schmid CH.

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